1. Field of the Invention
The present invention relates to a sheet conveyer having a sheet aligner or register, and more particularly to a sheet conveyer in an image forming apparatus such as a copying machine or printer. Furthermore, it relates to a sheet conveyer having an aligner for aligning a sheet widthwise before the sheet is guided to an image forming apparatus having a path along which the sheet is reconveyed to an image forming position in a both-surface multiple copy machine.
2. Related Background Art
A prior art apparatus is explained with reference to FIGS. 1A and 1B.
In this apparatus, a sheet is guided along a refeed or reload path in order to form images on front and back surfaces of the sheet.
In FIG. 1B, the sheet having an image recorded on a first surface thereof is fed from the right along an arrow 15, the image is fixed by a fixing unit 3, and the sheet is switched back by rollers 4 and 5 of roller unit 6 and fed along the direction of arrow 18. The sheet is reversed by a refeed path and again guided to the image forming unit where an image is recorded on a second surface The sheet is then ejected to a tray by rollers 4 and 4.
In this apparatus, since the left edge of the print sheet when the print sheet is fed along the direction of arrow 18 and a reference plane of the lateral registration are on the same line, no problem occurs when the sheet skews rightward with respect to the feed direction. However, if the sheet skews leftward even a bit, it abuts against a front plane 14a of the lateral registration plate and the sheet may be folded or jam. It may be theoretically possible to feed the print sheet without any skew but it is actually very difficult because very high precision parts are required. As shown in FIGS. 1A and 1B, the prior art apparatus is provided with an preliminary shift mechanism 23 to skew the print sheet oppositely to the lateral registration plate so that the print sheet is offset from the lateral registration plate and in parallel therewith. The print sheet is then caused to abut against the lateral registration plate by skew rollers 7 and 8 for alignment.
In the prior art apparatus, since the preliminary shift mechanism 23 is separately provided between the switch-back mechanism 6 and the skew mechanism 9, the number of parts is considerably large. The overall apparatus is complex and the size of the apparatus must be large because there must be a sufficient spacing to skew the print sheet between the switch-back mechanism and the preliminary shift mechanism, and between the preliminary shift mechanism and the skew roller mechanism. Accordingly, in the prior art apparatus, there are disadvantages of complexity, large size and resulting high cost.